1. Field of the Invention
The invention relates to a communication apparatus for communicating by using a light.
2. Related Background Art
In recent years, communication apparatus for communicating by using a light has widely been put into practical use. There are various kinds of communication apparatuses such as an apparatus using a spatial transmission, an apparatus using an optical fiber, an apparatus for communicating by coming into contact with another apparatus, and the like.
In such conventional communication apparatuses, a light emitting device is driven by a predetermined light intensity (at least, in terms of an assumption such that the light intensity cannot be purposely changed) irrespective of a type of transmission path.
The light intensity is set to an intensity sufficient enough to assure the communication at the time of the maximum attenuation on the transmission path (for instance, in case of the apparatus using the optical fiber, the maximum length; in case of the apparatus for performing the spatial transmission, the maximum distance).
A light emitting device (light emitting diode, laser diode, or the like) which is used for light communication is driven by a current of about tens of mA to 150 mA. However, since a low electric power consumption of an electronic apparatus is progressively realized nowadays, there is a tendency such that a ratio of the electric power consumption of the light emitting device to the electric power consumption of the whole apparatus is increasing. Therefore, as in the foregoing conventional apparatuses, a method whereby the light emitting device is always driven by the light intensity corresponding to the maximum attenuation is very disadvantageous from a viewpoint of the realization of a low electric power consumption.
In case of the apparatus for communicating by coming into contact with another apparatus, an interval between the light emitting device and the photosensitive device is set to a predetermined distance and no problem occurs even if the light intensity is inherently set to a fixed value. However, in many cases, the light intensity is set to a slightly higher value in order to cope with a variation among devices, a deviation of the light axis at the time of installation, or the like. The apparatus is also not driven by the optimum light intensity.
To solve the above problems, there is considered a method whereby light intensity measuring means for measuring the light intensity is provided on the photosensitive device side and the measurement result of the light intensity measuring means is fed back to the light emitting device side, thereby setting the light intensity to a proper value. According to such a method, however, there is a problem such that not only light emission intensity varying means for varying the light emission intensity on the transmission side is provided but also the light intensity measuring means has to be provided on the reception side.